1. Field of the Invention
The present invention relates to a forced-convection heat exchanger for rotary electrical machines.
2. Discussion of the Background
More particularly, the invention relates to a forced-convection heat exchanger of the compact type for a rotary electrical machine such as an electric motor.
Rotary electrical machines are traditionally plagued by significant losses due to the Joule effect in the stator elements (copper and iron) and due to the viscous friction between the surfaces and the fluid that circulates in the space between the rotor and the stator of rotary electrical machines.
This situation worsens as the rotation rate of the machines rises.
According, it is necessary to provide a cooling system which is capable of dissipating the generated heat and of ensuring that the maximum temperatures reached by the rotor and the stator are such as to avoid degrading the electromechanical performance of the materials that are typically used.
For example, for a permanent-magnet motor, the permanent magnets must not reach excessively high temperatures, on penalty of losing or degrading their magnetic properties.
The system must also typically work within clearly defined temperature values which are generally rather low in order to have low costs.
The heat exchanger must also be compact and highly efficient. The problem of removing the heat generated by an electrical machine is currently dealt with in various manners.
The main technique consists in using fins which are struck by a stream of air generated by a fan and are arranged on the shell of the machine or inside it according to the various configurations.
When a fluid is used for cooling, the motor is enclosed with a jacket inside or outside which the fluid is made to pass through appropriately shaped passages. Cooling can affect both the stator, as is usually the case, and the rotor, and in this case cooling generally occurs by a static exchanger arranged around the rotor.
The effectiveness of the exchanger is more important in high-speed machines with dimensions that must be compact and in which accordingly the dimensions of the auxiliary components, such as the heat exchanger, cannot exceed certain values.
Two kinds of heat exchangers are generally used in conventional electrical machines.
A first type has a constant cross-section, in which the flow is generally laminar. In order to increase the efficiency of this heat exchanger, it is necessary to increase the speed so as to produce turbulent motion conditions. This type entails a significant increase in pressure losses and entails higher pumping costs.
A second type is the one in which the motion is rendered turbulent by inserting appropriate obstacles. This solution has the advantage of increasing heat exchange efficiency for an equal flow-rate of the cooling fluid. Despite the fact that the presence of obstacles increases pressure losses, accordingly requiring once again to use pumping elements capable of propelling the fluid under high pressure differentials, this solution is generally more efficient than the preceding one.
The aim of the present invention is to provide a forced-convection heat exchanger for rotary electrical machines which is highly efficient and capable of removing the considerable thermal energy levels generated in the stator and rotor elements of the electric motor. Within the scope of this aim, an object of the present invention is to provide a forced-convection heat exchanger which is particularly compact and therefore suitable for electric motors which are compact but have a high specific power level.
Another object of the present invention is to provide a forced-convection heat exchanger for motors which exchanger allows one to remove heat from the regions of the electric motor where it is generated most.
Another object of the present invention is to provide a forced-convection heat exchanger which allows one to keep the temperature of the inner face of the stator, which is the most critical one, at an acceptable level in accordance with the characteristics of the materials used.
Another object of the present invention is to provide a forced-convection heat exchanger which also allows one to maintain low temperatures on the surface of the rotor.
Another object of the present invention is to provide a forced-convection heat exchanger which is highly reliable and relatively easy to manufacture at competitive costs.
Thus, the present invention provides a forced-convection heat exchanger for a rotary electrical machine, comprising one or more tubing elements that are arranged between the conductors of the stator windings of said rotary electrical machine so as to be in contact with the outer surface of said conductors with a cooling fluid flowing into said tubing elements.